The present invention relates to a lamp device using LEDs (Light Emitting Diodes) for purposes of indication or illumination, and more particularly, to an LED lamp device which can be directly connected (directly coupled) to an alternating-current power supply.
Incandescent lamps using a tungsten filament are still popular for use as various indicator lamps installed in buildings for offices, condominiums, public facilities, etc., such as fire hydrant lamps or emergency lamps, and also as operation button lamps of ticket vending machines and other vending machines, elevators, etc. Further, not a few interior lighting fixtures still use incandescent lamps depending on their purposes.
With the recent advance of semiconductor device technology, LEDs have come to have performance superior to that of incandescent lamps, in terms of the diversity of luminescent color, luminance, durability, and power consumption (luminous efficacy). Nevertheless, at present LEDs are scarcely used for the aforementioned purposes.
This is because lamps for indication or illumination purposes are usually put to use on condition that they are directly connected to commercial alternating-current power supply (100 V in Japan, 110 V in the United States, 230 V in Europe).
Namely, as is generally known, an LED operates with several volts of direct-current (DC) power supply voltage. Thus, in order to use conventional LEDs for the above purposes, it is necessary that a special power supply unit be provided to convert the commercial alternating-current power to several volts of DC voltage, but this makes the LED lamp device expensive and increases the overall size.
Despite these shortcomings, attempts have conventionally been made to connect LEDs directly to the commercial alternating-current power supply, as explained below with reference to the drawings.
FIG. 23 is a circuit diagram showing an LED lamp device of Conventional Type 1.
In FIG. 23, reference numeral 2003 denotes an AC input terminal H (HOT LINE), 2004 denotes another AC input terminal C (COOL LINE), 2002 denotes a full-wave rectifying diode bridge (BrD1), 2005 denotes a series resistor (Rp), 2006 denotes a constant-current element (CRD: Current Regulated Diode), and 2007 denotes an LED lamp.
The LED lamp 2007 usually comprises two to eight serially connected LEDs each having a VF value (forward voltage drop) of about 2 V, and accordingly, a total VF value is 4 to 16 V. The peak voltage of the fully rectified wave supplied from the diode bridge 2002 is approximately 140 V in the case of the commercial power supply in Japan whose root-mean-square value is 100 V.
Provided that an IF value (forward current) of the LED lamp for attaining the required luminance is about 10 mA and that the LED lamp is constituted by one LED, the voltage borne by the resistor 2005 and the constant-current element 2006 is: 140 Vxe2x88x922 V=138 V, since VF is 2 V, and 138 Vxc3x9710 mA=1.38 W is consumed by heat dissipation.
The electric power that contributes to light generation is: 2 Vxc3x9710 mA=0.02 W, and the luminous efficacy is:
xe2x80x830.02W/(1.38W+0.02W)=0.014
Thus, the luminous efficacy is as low as 1.4%, showing that nearly 99% of the electric power is lost by heat dissipation.
FIG. 24 is a circuit diagram showing an LED lamp device of Conventional Type 2.
In FIG. 24, reference numeral 2105 denotes a voltage regulator (Vreg1), and 2106 denotes a current-limiting resistor (Rc). Also in FIG. 24, identical reference numerals are used to denote elements identical with or equivalent to those appearing in FIG. 23.
In Conventional Type 2, variations in voltage of the fully rectified AC wave are balanced by the voltage regulator 2105; therefore, the constant-current element CRD used in the aforementioned Conventional Type 1 can be omitted and also the light generation is stabilized. However, the efficiency of electric power utilization is basically the same as (as low as) the aforementioned Conventional Type 1, because of the series regulation of voltage.
As described above, the conventional devices are low in efficiency and high in loss, and thus there has been a demand for a device improved in these respects.
An object of the present invention is therefore to provide a power supply unit and an LED lamp device which are high in efficiency and low in loss.
To achieve the above object, a power supply unit according to a first aspect of the invention comprises: wave rectifier operable to obtain a rectified wave of an alternating-current power supply voltage; and an electric power output operable to admit electric power for only part of a time period in which a voltage of the rectified wave obtained by the wave rectifier and corresponding to each half period of a wave of the alternating-current power supply voltage is higher than or equal to a predetermined value, and to output the electric power as power for driving a load.
A power supply unit according to a second aspect of the invention comprises: a rectifying diode bridge operable to obtain a rectified wave of a power supply voltage; an oscillator circuit; a clock signal control circuit; and a switched capacitor step-down circuit including a plurality of changeover switches connected in series and capable of being switched between two positions, and a capacitor connected between adjacent ones of the changeover switches, wherein the changeover switches are switched to either of the two positions by the clock signal control circuit such that the capacitors are charged when the changeover switches are in one of the two positions and that the capacitors are discharged when the changeover switches are in the other of the two positions, thereby supplying electric power to a load.
A power supply unit according to a third aspect of the invention has two input terminals connected to an alternating-current power supply, for supplying electric power to a load connected to output terminals thereof. The power supply unit of this aspect comprises: an oscillator circuit; a clock signal control circuit; a current detection circuit; and two switched capacitor step-down circuits, wherein a high voltage-side input terminal of one of the two switched capacitor step-down circuits and a low voltage-side input terminal of the other switched capacitor step-down circuit are connected to one of the two input terminals of the power supply unit, and a low voltage-side input terminal of said one switched capacitor step-down circuit and a high voltage-side input terminal of the other switched capacitor step-down circuit are connected to the other of the two input terminals power supply unit.
An LED lamp device according to a fourth aspect of the invention comprises: a power supply unit supplied with an alternating-current power supply voltage; and an LED lamp including one or a plurality of serially connected LEDs connected to output terminals of the power supply unit, wherein the power supply unit obtains a rectified wave of the alternating-current power supply voltage, admits electric power for only part of a time period in which a voltage of the rectified wave corresponding to each half period of a wave of the alternating-current power supply voltage is higher than or equal to a predetermined value, and uses the electric power as power for lighting the LED lamp.
Preferably, in the LED lamp device according to the fourth aspect of the invention, the power supply unit includes a rectifying diode bridge and a Zener diode serving as a constant-voltage element and connected in series with the rectifying diode bridge, wherein the diode bridge rectifies the input voltage and then the Zener diode admits the electric power for only the time period in which the rectified voltage is higher than or equal to the predetermined value, to light the LED lamp.
An LED lamp device according to a fifth aspect of the invention comprises: a power supply unit supplied with alternating-current or direct-current power; and an LED lamp including one or a plurality of serially connected LEDs connected to output terminals of the power supply unit, wherein a Zener diode is connected in parallel with the one or plurality of LEDs.
Preferably, in the LED lamp device according to the fifth aspect of the invention, where the LED lamp comprises a plurality of LED lamps, a constant-current element is connected to the output terminals of the power supply unit in series with the LED lamps. With this arrangement, even in the event any of the LED lamps burns out and thus turns off, the remaining LED lamps can remain on.
Also preferably, in the LED lamp device according to the fifth aspect of the invention, the Zener diode has a Zener voltage higher than a forward voltage drop of the LED lamp connected in parallel with the Zener diode within a range of from 10% to 30% both inclusive. If the difference between the Zener voltage and the forward voltage drop is smaller than 10%, dimming cannot be effectively prevented, and if the difference is greater than 30%, the LED lamp cannot be fully protected from overcurrent.
An LED lamp device according to a sixth aspect of the invention comprises: a power supply unit supplied with an alternating-current or direct-current power supply voltage; and an LED lamp including one or a plurality of serially connected LEDs connected to output terminals of the power supply unit, wherein the power supply unit includes a current detection circuit, an input voltage detecting section, an oscillator circuit, a switching circuit and a switching element, and the switching circuit is supplied with signals from the current detection circuit and the input voltage detecting section to perform ON/OFF control of the switching element.
Preferably, in the LED lamp device according to the sixth aspect of the invention, the power supply unit obtains a rectified wave of the power supply voltage, admits electric power for only part of a time period in which a voltage of the rectified wave corresponding to each half period of a wave of the alternating-current power supply voltage is higher than or equal to a predetermined value, and uses the electric power as power for lighting the LED lamp.
An LED lamp device according to a seventh aspect of the invention comprises: a power supply unit supplied with alternating-current or direct-current power; and an LED lamp including one or a plurality of serially connected LEDs connected to output terminals of the power supply unit, wherein the power supply unit includes an input/output voltage detecting section, an oscillator circuit, a switching control circuit, a switching element and a current detection circuit, and the switching control circuit is supplied with signals from the input/output voltage detecting section and the current detection circuit to perform ON/OFF control of the switching element.
An LED lamp device according to an eighth aspect of the invention comprises: a power supply unit supplied with alternating-current or direct-current power; and an LED lamp including one or a plurality of serially connected LEDs connected to output terminals of the power supply unit, wherein the power supply unit includes a rectifying diode bridge, a current detection circuit, an input voltage detecting section, an oscillator circuit, a switching circuit and a switching element, the switching circuit is supplied with signals from the current detection circuit and the input voltage detecting section to perform ON/OFF control of the switching element, and a capacitor is connected between the switching element and the LED lamp such that the capacitor is charged when the switching element is in an ON state and that electric power is supplied to the LED lamp from the capacitor when the switching element is in an OFF state.
An LED lamp device according to a ninth aspect of the invention comprises: a power supply unit supplied with an alternating-current or direct-current power supply voltage; and an LED lamp including one or a plurality of serially connected LEDs connected to output terminals of the power supply unit, wherein the power supply unit includes a rectifying diode bridge for obtaining a rectified wave of the power supply voltage, an oscillator circuit, a clock signal control circuit and a switched capacitor step-down circuit, the switched capacitor step-down circuit includes a plurality of changeover switches connected in series and capable of being switched between two positions, and a capacitor connected between adjacent ones of the changeover switches, and the changeover switches are switched to either of the two positions by the clock signal control circuit such that the capacitors are charged when the changeover switches are in one of the two positions and that the capacitors are discharged when the changeover switches are in the other of the two positions, thereby lighting the LED lamp.
An LED lamp device according to a tenth aspect of the invention comprises: a power supply unit supplied with alternating-current power; and an LED lamp including one or a plurality of serially connected LEDs connected to output terminals of the power supply unit, wherein the power supply unit includes an oscillator circuit, a clock signal control circuit, a current detection circuit and two switched capacitor step-down circuits, a high voltage-side input terminal of one of the two switched capacitor step-down circuits and a low voltage-side input terminal of the other switched capacitor step-down circuit are connected to one of two input terminals of the power supply unit, and a low voltage-side input terminal of the one switched capacitor step-down circuit and a high voltage-side input terminal of the other switched capacitor step-down circuit are connected to the other of the two input terminals of the power supply unit.
In the aforementioned arrangements according to the invention, the power supply unit is preferably mounted on a flexible printed circuit board, and the flexible printed circuit board is bent into a generally S-shaped form. Preferably, moreover, the power supply unit has terminals attached to opposite sides of the generally S-shaped form of the flexible printed circuit board, and has two AC input terminals attached to opposite surfaces of the flexible printed circuit board. This arrangement makes it possible to save space, to ensure high insulating performance, and also to improve the characteristics and reliability of the device.
Also preferably, the power supply unit generates a pulsed current having a peak current value higher than a set average current value, and the pulsed current has a frequency of not lower than 100 Hz. This arrangement makes it possible to increase the luminance perceivable by human with the use of less electric power.
According to the first to fourth and sixth to tenth aspects of the invention, the power supply unit is constructed such that electric power is admitted for only part of a time period of the power supply voltage cycle and is output as power for driving a load, thus providing a high-efficiency and low-loss power supply unit capable of driving an LED lamp with the use of a desired voltage higher than the power supply voltage, as well as an LED lamp device using such a power supply unit.
According to the fifth aspect of the invention, a high-efficiency and low-loss LED lamp device can be provided wherein dimming can be prevented and also the LED lamp can be protected from overcurrent.